The Northcroft monitoring station is not, to look at, a building one would associate with the leading edge of geological enquiry. It is a single-room hut, fourteen feet by ten, set into the lee slope of the Greymoor ridge approximately 340 metres south of the principal emission point, with a corrugated iron roof painted a dark green that does not interfere with night observations from the road. The hut contains: one steel desk, two wooden stools, a kerosene lamp (rarely used), a paraffin stove (frequently used), a kettle, two enamel mugs, a portable barometer, and the recording instruments themselves, which occupy approximately a third of the floor space and which run on batteries supplied by a small wind generator on the ridge above.

The instruments are: three thermistor probes set at depths of 50 cm, 1.5 m, and 3 m at each of the four emission points (twelve probes in total); two single-axis fluxgate magnetometers, one fixed at the hut and one mounted on a tripod that is moved along the ridge daily; one short-period seismometer, recording continuously to a paper drum that must be replaced every forty-eight hours; and a simple mercury thermometer hung outside the hut door for the recording of ambient air temperature. The whole assemblage was installed by Gerald Northcroft and his daughter Imogen between the 16th and the 18th of April, working long days in cold weather. They were observed throughout by Gareth Penn, sheep farmer of Highfield Farm, who brought them tea twice a day and who said, on the morning of the 18th, that the dog had stopped staring at the ridge.

The first eight days of data are now in. Imogen Northcroft, twenty-six, who has been operating the station alone since the 19th and who is currently the only person in Bobington (she points out, with a slight smile, that this makes her the only person in Bobington tied with the only person at Caldwell) to have read the data continuously for more than a week, presented her preliminary findings to the Polytechnic geology committee on Friday morning. She brought the data in three loose-leaf folders. She had not slept much.

The findings, in brief:

Temperature. The four emission points show soil temperatures, at 50 cm depth, of between 14.4 and 17.2 degrees Celsius. Background soil temperatures, recorded at four control sites between 200 and 800 metres from the nearest emission point, range from 7.8 to 9.1 degrees. The differential is between six and nine degrees, depending on the point. The 1.5-metre and 3-metre probes show smaller but still elevated temperatures: approximately three to five degrees above background at 1.5 m, and approximately one to two degrees above background at 3 m. This temperature profile, Imogen Northcroft told the committee, is consistent with a heat source at substantial depth — at least several hundred metres — supplying a low but continuous heat flux to the surface through fractured rock.

It is not, she emphasised, consistent with a magma body close to the surface. There is no shallow heat source at Greymoor. The intrusion, if Professor Nettleford is correct that one exists at approximately 800 metres’ depth, is providing a slow conductive flux through the overlying granite.

“It is warming the rock,” she said. “It is not melting it. The distinction matters.”

Magnetism. The magnetometer surveys, conducted along a 3-kilometre line between the northern and southern ends of the visible emission zone, have identified a weak but stable magnetic anomaly along the central 1.2 kilometres. The anomaly is on the order of 50 to 80 nanoteslas — small enough that it would not be detected without instruments of this sensitivity, large enough to be clearly distinguishable from background variability. The anomaly is consistent with the presence of magnetic minerals — most likely magnetite or pyrrhotite — in altered rock at depth. This is, Northcroft noted, exactly what one would expect at the upper margin of an igneous intrusion in a granitic country.

“It is, I am afraid, not a coincidence,” she said. The committee laughed.

Seismicity. The seismometer has recorded twenty-three discrete events in eight days, all of magnitude less than 1.5, all at depths estimated between 600 and 1,100 metres, all clustered within a 4-kilometre radius of the central emission zone. The events are small. They are not felt at the surface. They are, however, occurring at a rate of approximately three per day, where the regional background rate for the Bobington uplands is approximately one event per fortnight.

“There is something moving down there,” Imogen Northcroft said. “It is moving slowly. It has been moving for at least the duration of our recording. We do not yet know whether it has been moving for longer than that, because there are no prior instruments. But the pattern is consistent and the depth is consistent and the temperatures are consistent, and we are now reasonably confident that we are observing a single coherent system.”

The committee — chaired by Dr Margaret Collis of the Polytechnic geology department, with five members present and three by written submission — asked questions for ninety minutes. The questions ranged from the entirely technical (Dr Wilbraham wanted to know whether the magnetometer drift had been compensated for diurnal solar variation; it had) to the practical (Dr Ilkley asked whether the elevated soil temperatures would affect the surrounding pasture; the answer, on present evidence, was no, though it might affect the timing of spring growth at the immediate emission points).

The most interesting question came from a junior committee member, the geophysicist Aurelia Crowne, twenty-nine, recently arrived from a postdoctoral position in Edgeminster. She asked: “If the heat flux is conductive through fractured rock, and the seismicity is at depths between six hundred and eleven hundred metres, are we observing the slow propagation of a fluid front through an existing fracture network, or are we observing the slow opening of new fractures?”

Imogen Northcroft hesitated.

“I do not know,” she said. “I think Professor Nettleford may have an opinion. I would like to hear it.”

She will hear it on Wednesday evening. Professor Aldous Nettleford of the University of Caldwell, whose 15 April lecture at the Polytechnic on the Greymoor system filled the Founders’ Hall to standing capacity and was extended by twenty-five minutes for questions, has confirmed his return for the closing lecture in the spring public series. He will travel from Caldwell on Tuesday’s afternoon express, arriving at Bobington Central at 7:42 PM, and will be met at the station by Director Aldbury and by Imogen Northcroft, who has been corresponding with him since the 19th and who has, by her own account, sent him three sets of data summaries and received in return three pages of careful, polite, and devastatingly precise questions.

The closing lecture is at 7:30 PM on Wednesday the 29th, in the Founders’ Hall. The title — submitted by Nettleford on Friday morning by telegram from Caldwell — is “Greymoor: What We Now Know, and What We Still Do Not.” Tickets are not required. Director Aldbury has arranged for additional standing places at the back of the hall, and for the lecture to be reproduced in its entirety in the Polytechnic Annual Bulletin.

The glow above the ridge, on Friday night, was in its eighty-fourth consecutive night. It was, by the unaided eye, slightly brighter than it had been on Monday. Whether this is a real change or a function of clearer air, no one is yet prepared to say. Imogen Northcroft has begun a separate set of nightly photographic exposures, using a Polytechnic-supplied plate camera fixed on a tripod beside the hut. The first six plates have been developed. The committee will examine them next week.

Gareth Penn, asked on Friday afternoon what he made of all of it, said that the dog still wasn’t staring at the ridge.

“That’ll do for me,” he said.